1. Field of the Invention
The present invention relates generally to a permanent magnet arrangement for magnetron plasma processing and more specifically to such an arrangement for magnetically confining plasma in order to implement magnetron ion sputtering. The present invention is also applicable to magnetron ion etching as well.
2. Description of the Prior Art
It is known in the art to use enhanced magnetron plasma for fabricating electronic devices by sputtering or etching, wherein a magnetically confined plasma is effectively utilized to attain high ion densities and low ion energies.
Before turning to the present invention it is deemed advantageous to briefly discuss a magnetron sputtering apparatus with reference to FIGS. 1-6.
FIG. 1 is a diagram schematically showing a magnetron sputtering apparatus which is enclosed in a chamber case or housing although not shown. FIG. 2 is a plan view of a magnetic field generator of the apparatus 8.
In FIG. 1, the magnetron sputtering apparatus, depicted by numeral 8, includes an anode 10 and a cathode 12 which are arranged parallel with each other. The anode 10 is grounded and carries a substrate 14 on which sputtered material is deposited. On the other hand, the cathode 12 is coupled to an RF (radio frequency) power source 15 and carries thereon a target 16 which is a solid piece of the material to be deposited. Further, a magnetic field generator 18 is attached to the bottom of the cathode 12.
As best seen in FIG. 2, the magnetic field generator 18 includes a yoke 20 on which an annular permanent magnet 22 and a cylindrical permanent magnet 24 are concentrically provided. These magnets 22 and 24 are magnetically arranged in the illustrated manner. In FIG. 1, magnetic field lines denoted by numeral 26 are generated between the magnets 22 and 24, while a solid arrow 28 represents the direction of electric field.
When electric discharge is established between the electrodes 10 and 12 in an environment containing Argon gas (for example), a plasma (viz., a highly ionized gas) is generated. As is well known in the art, electrons move under the combined force of an electric field and a magnetic field along cycloid curves and further enhance ionization. The drift applied to the electrons results from the magnetic field which is parallel to the surface of the target (viz., the magnetic field perpendicular to the electric field). Therefore, in order to effectively drift the electrons for the purposes of further ionizing plasmas, it is vital to uniformly generate the components of the magnetic field which are parallel to the surface of the target 16.
Merely for the convenience of description, the components of the magnetic field parallel to the surface of the target 16 may sometimes be referred to as parallel or horizontal magnetic field.
FIG. 3 is a diagram schematically showing the manner wherein an electron 32 is drifted along a cycloid curve 34 under the combined force of an electric and magnetic fields as mentioned above. This physical phenomena is well known in the art and hence further discussion thereof will be deemed redundant.
The permanent magnet arrangement shown in FIGS. 1 and 2, however, has encountered the drawback in that the magnitude of the horizontal magnetic field varies across the surface of the target 16. Thus, a highly ionized plasma is unable to be generated over a wide area of the target 16. This means that the target 16 is sputtered at only the portions where the horizontal magnetic field is exhibited. That is, the target is partially consumed or sputtered. This partial consumption of the surface of the target leads to the fact that the life of the target 16 is undesirably shortened and thus decreases the efficiency of utility thereof.
In order to overcome the above mentioned drawbacks, several permanent magnet arrangements have been proposed.
FIG. 4 shows one of the known approaches to overcoming the aforesaid drawbacks. As shown, there are provided a central cylindrical magnet 36 and two annual magnets 38 and 40, all of which are concentrically arranged on a yoke 42 having the same diameter as the outer magnet 40. This arrangement, however, has suffered from the problem that the magnetic field is perpendicular to the surface of the yoke 42 at the center and peripheral portions and thus, the components of the magnetic field, which are parallel to the surface of a target to be provided adjacent to the arrangement of FIG. 4, are not expected over a wide area of the surface of the target.
FIG. 5 shows another known permanent magnet arrangement which includes a semi-cylindrical magnet 50 which is surrounded by a D-shaped magnet 52. These magnets 50 and 52 are placed on a yoke 54 with the poles arranged in the illustrated manner. On the other hand, FIG. 6 illustrates still another conventional permanent magnet arrangement which includes an eccentrically provided magnet 56 which is surrounded by two irregularly shaped closed magnets 58 and 60. These magnets 56, 58 and 60 are provided on a yoke 62 in the illustrated manner.
With the arrangements shown in FIGS. 5 and 6, in order to generate horizontal magnetic field on the corresponding target, each of the yokes 54 and 62 should be rotated around the axis thereof. Thus, the prior art techniques shown in FIGS. 5 and 6 have suffered from the following drawbacks:
(a) a magnetron sputtering apparatus is inevitably rendered complex in that appropriate rotation mechanism is required to revolve the yokes 54 or 62 around the axis thereof;
(b) the interior of the apparatus is apt to become contaminated by fine particles produced from the rotating mechanism; and
(c) the manufacturing of the magnet arrangement on the corresponding yoke is relatively expensive due to the complex configuration.
It is therefore highly desirable to overcome the aforesaid prior art difficulties with a simple arrangement of permanent magnets.
The foregoing has been made with the magnetron sputtering where the magnetic field generator 18 is placed adjacent to the target 16. In contrast, the magnetic field generator 18 is located in the vicinity of the substrate 14 in the case of magnetron etching. The instant invention is applicable to both the magnetron sputtering and etching as well.